Affiliates commissions, worth n months from subscribed plan
Two main affiliate commission models in WHMCS currently are either flat monthly fee or percentage from monthly invoice. What is missing - default commissions worth of n months from subscribed plan. Ideally it should be defined as extra option in General Settings - > Affiliate window.
Not streamlined option as it is today (see attached picture):
For each product (whilst editing the product itself) navigate to the other tab and set the Custom Affiliate Payout to Fixed Amount then in the Affiliate Pay Amount box enter the amount that this affiliate will receive (so the first months cost of the product you are editing) and finally tick the One Time Payout checkbox so this is only paid once.